In recent years, the nasal passageway has been gaining attention as an alternate route of administration for systemically active drugs, such as peptides and proteins. Some proteins, such as intracellular adhesion molecule ICAM-1, are best delivered via the nasal passageway.
The desired size range of microparticles that maybe used to deliver drugs via the nasal passageway is fairly narrow, i.e., diameters of between about 20 μm and 80 μm. If the microparticles are too small, i.e., less than about 10 μm, they can be carried with the airstream down into the tracheobronchial region. Thus, microparticles having diameters of less than about 10 μm could be used to deliver drugs via the tracheobronchial passageways. If the microparticles are too large, i.e., greater than about 100 μm, then the microparticles are relatively rapidly cleared from the nasal passageway.
Drug delivery to the nasal mucosa, for either topical or systemic action, is influenced by the duration of the contact with the drug-loaded particles. Nasal spray preparations administered using pumps or pressurized metered dose inhalers deposit mainly in the anterior part of the nasal cavity. That region is largely non-ciliated, and clearance is relatively slow. Generally, mucociliary function clears materials from the turbinates into the nasopharynx on average at a rate of about 6 mm/minute, with the flow rate increasing posteriorly. Nasal clearance depends on the particle size of the drug-loaded particles and the deposition site within the nasal passageway. Particles deposited in the sparsely ciliated or non-ciliated anterior region of the nasal cavity are cleared at a slower rate due to a slow drag from the contiguous mucus.
The majority of human rhinoviruses, the major causative agent of the common cold, utilize intercellular adhesion molecule 1 (ICAM-1) as a receptor on host cells. ICAM-1 is an integral membrane protein with a large N-terminal extracellular portion, a transmembrane anchor, and a short C-terminal cytoplasmic domain. The normal physiological function of ICAM-1 is to serve as a membrane-bound ligand of the leukocyte integrin lymphocyte function-associated antigen 1 (LFA-1) and mediate intercellular adhesion between leukocytes and a variety of cell types. (See, Greve et al., “Mechanisms of Receptor-Mediated Rhinovirus Neutralization Defined by Two Soluble Forms of ICAM-1”, J. Virol. 65(11):6015-6023 (1991)). Since ICAM-1 binds human rhinovirus, a truncated form of ICAM-1, t-ICAM-453, has been proposed for clinical use as a nasally delivered prophylactic for rhinovirus infections. It would be desirable to minimize the need for repeated administration by providing increased ICAM-1 dwell-time in the nasal cavity.
The technology of microparticle production has extensive applications for drug delivery. A number of techniques have been utilized to make such microparticles, including solvent evaporation, and spray drying. One of the simplest presently available techniques is the preparation of calcium alginate microparticles by extruding or spraying sodium alginate solution as droplets into a calcium chloride solution.
The acceptability of microparticles for controlled release of drugs, including proteins, in the nasal passageway requires a product that is small in diameter, i.e., considerably less than one millimeter, that may be manufactured in a consistent size and drug distribution, and that has controlled degradation properties.
One method for manufacturing calcium alginate microparticles is to disperse the aqueous sodium alginate solution containing drug in an organic phase, then add calcium chloride to harden the emulsion formed droplets. In one such batch-process, a 3:2 ratio of two surfactants (sorbitan trioleate and polyoxyethylene sorbitan trioleate) and a minimum concentration of approximately 1% weight/weight (w/w) of surfactant is required to be added to the mixture to produce acceptable drug-loaded particles. (See, e.g., Wan et al., “Drug Encapsulation in Alginate Microspheres by Emulsification.” Microencapsulation 9(3):309-316 (1992)). Other surfactant mixture ratios or concentrations may affect the microparticle size, shape, degree of clumping, drug loading and drug release characteristics. Thus, this method of preparing calcium alginate microparticles is sensitive to surfactant types and concentrations.
In batch process emulsion formation and hardening techniques, surfactants commonly are required to improve the microparticle size/shape and drug encapsulation efficiency. Problems likely to arise as a result of using such surfactants include: difficulty in washing the surfactants out of the formulation and measuring residual levels; possible adverse health effects caused by any residual surfactants; difficulty in washing the surfactants out of the formulation while not leaching out the drug; and potential effects on the bioadhesion, swelling behavior, and drug release profile of the microparticle.
Spray droplet formation techniques for manufacturing microparticles tend to produce large particles, i.e., over one millimeter (1 mm) in diameter. Although spray droplet formation techniques could be used to produce microparticles in the desired size range of between about 20 μm and 80 μm, this droplet formation technique is not desirable due to the difficulty in scaling the technique, process variability, and lack of suitability to clean pharmaceutical processing.
Numerous chemicals, polymers and controlled-release agents that may be used in manufacturing microspheres are known and commercially available. Examples of materials used to prepare microspheres for nasal delivery are: cellulosic polymers, specifically lower alkyl ethers of cellulose, starch, gelatin, collagen, dextran and dextran-derivatives, protein polymers, such as albumin, disodium cromoglycate, sephadex, or DEAE-sephadex. These may include mixtures or coatings with other materials such as polyacrylic acids, to improve the bioadhesive or controlled-release properties of the microspheres. (See, e.g., U.S. Pat. No. 5,204,108 to Illum.)
Other materials that may be used in manufacturing microparticles are known and include alginates, xanthan gum, and gellan gum, among others. All three substances are effective as enteric coatings. Alginates are known to produce uniform films, with application in industries as diverse as paper coatings, textile printing, and foods. The alginate film is particularly useful as an enteric coating because it normally is applied as the soluble sodium form, which then is converted to the insoluble alginic acid form by gastric fluids. Improvements have been made by combining sodium alginate with sodium calcium alginate in tablets containing high drug loading.
Alginates also have been used in fluid suspensions for many years because of their ability to form a gel upon contact with gastric fluids. Furthermore, calcium alginate gel beads are used to contain a variety of substances, such as flavors in the food industry, enzymes for bioreactors, live cells, and live organisms. Calcium alginate is particularly favored because of the mild conditions employed in its manufacture and the nontoxicity of the reagents.
Alginate is a collective term for a family of copolymers containing 1,4-linked β-D-mannuronic and α-L-guluronic acid residues in varying proportions and sequential arrangement. Alginate forms gels with divalent ions like calcium, and the gel-forming properties are strongly correlated with the proportion and lengths of the blocks of contiguous L-guluronic acid residues in the polymeric chains. The properties of alginates are described in Martinsen et al., “Alginate as Immobilization Material,” Biotechnol Bioeng. 33:79-89 (1989).
Although there are several reports of using alginate beads to microencapsulate peptides and proteins, nearly all reports indicate bead sizes over 100 μm in diameter. In addition, nearly all reports prepare alginate gel beads by dropping sodium alginate solution into an aqueous calcium chloride solution to form the beads. While such a method does produce microencapsulated beads, the difficulty in controlling operating conditions to produce microparticles in the desired size range, difficulty in scaling, and the lack of suitability to clean pharmaceutical processing makes such methods impractical for commercial production of microparticles containing proteins such as ICAM-1.
The preparation of drug-loaded microspheres is described generally in U.S. Pat. No. 5,204,108 to Illum. In that patent, active agents are incorporated into microspheres made from gelatin, albumin, collagen, dextran and dextran-derivative. The final microspheres are cross-linked and finally processed for transmucosal delivery. However, there remains a need for microspheres that deliver a drug to the nasal passageway for controlled, long-term release of the drug in the passageway and that neither cross the mucosal barrier nor are cleared from the passageway.
Thus, there remains a need for a method and system for producing microparticles loaded with drugs, peptides or proteins that may be used for controlled, sustained release of the drug or protein. The preferred method and system should reliably produce microparticles for delivery of drug into the nasal passageway that have a predictable load, that are within a size range of between about 20 μm and about 80 μm, with about an 80% to about 100% recovery, and without significant loss in drug efficacy.